Self-contradicting words
The Wikipedia is a good source of unusual lists. I accidentally came across the List of self-contradicting words in English. It's interesting to speculate on how these meanings came about.
Bolt As a transitive verb, it means "to secure something in place (with a bolt)". But as an intransitive verb, it means "to leave or run away from (quickly)".
Buckle As a verb construction of the noun buckle, which is a device for clasping a belt together, it means "to secure, tighten, hold"; otherwise, it means "to weaken, collapse".